Don't crash if old build products are absent (fixup for 87d6040)
Don't crash if old build products are absent (fixup for 87d6040)

We no longer have an easy-install.pth file, so don't crash if it's not
found. This code will be removed once 87d6040 has been in stable for a
while.

jhuttner/dx-toolkit,dnanexus/dx-toolkit,dnanexus/dx-toolkit,johnwallace123/dx-toolkit,johnwallace123/dx-toolkit,jhuttner/dx-toolkit,jhuttner/dx-toolkit,jhuttner/dx-toolkit,jhuttner/dx-toolkit,jhuttner/dx-toolkit,jhuttner/dx-toolkit,johnwallace123/dx-toolkit,dnanexus/dx-toolkit,dnanexus/dx-toolkit,jhuttner/dx-toolkit,johnwallace123/dx-toolkit,dnanexus/dx-toolkit,dnanexus/dx-toolkit,johnwallace123/dx-toolkit,johnwallace123/dx-toolkit,dnanexus/dx-toolkit,dnanexus/dx-toolkit,johnwallace123/dx-toolkit,johnwallace123/dx-toolkit